The present invention relates to a method for the preparation of a sintered body of silicon carbide or, more particularly, to a method for the preparation of a sintered body of silicon carbide having excellent thermal conductivity and high electric insulation and useful as a material of substrates of integrated circuits and other electronic components.
Silicon carbide in the form of a sintered body is a material having various excellent properties such as heat resistance, wear resistance, mechanical strength, corrosion resistance and so on so that silicon carbide is highlighted in recent years as a material suitable for various applications. In particular, the high electric insulation and thermal conductivity of silicon carbide ensure the usefulness thereof as a material as the substrates of integrated circuits and other electronic components.
Technical difficulties are encountered, however, when further improvements are intended in the volume resistivity and thermal conductivity of sintered bodies of silicon carbide. Various attempts and proposals have been made hitherto in this regard including a method of admixing beryllium oxide to the silicon carbide powder prior to sintering. This method, however, is not practical in respect of the safety problem of workers due to the strong toxicity of beryllium compounds. In addition, beryllium oxide has little effect as a sintering aid so that the silicon carbide powder admixed with beryllium oxide can be shaped and fully sintered into a high-density sintered body only by use of a hot press because no satisfactory sintered body can be prepared by sintering under normal pressure. Moreover, the supply of beryllium compounds is relatively small and unstable in the world due to the scantiness of the resources if not to mention the expensiveness. Finally, sintered bodies of silicon carbide must be sliced and lapped in the manufacturing process of substrates for integrated circuits by using expensive tools so that the cost for the production of finished products is unavoidably increased so much.
Most of ceramic substrates for integrated circuits are made from aluminum oxide in view of the inexpensiveness thereof. Aluminum oxide-made ceramic substrates are disadvantageous, however, in respect of the low thermal conductivity of 20W/m.K and the considerably larger coefficient of thermal expansion of 8.times.10.sup.-6 /.degree.C. than the coefficient of thermal expansion 3.5.times.10.sup.-6 /.degree.C. of single crystals of semiconductor silicon. Accordingly, it has been eagerly desired to develop a material superior to aluminum oxide in respect of heat conduction and heat radiation. Besides silicon carbide, aluminum nitride is one of the candidate materials for the substrates of integrated circuits but the application fields of aluminum nitride-made substrates are disadvantageously limited due to the poor chemical resistance in addition to the inherently low thermal conductivity.